This paper describes a novel approach to the evaluation of anthropogenic impacts on flood risks in coastal
mega-cities by incorporating three anthropogenic variables (land subsidence, urbanization and flood
defence) within a scenario-based framework where numerical modelling was undertaken to quantify the
risks. The evolving risks at four time points (1979, 1990, 2000 and 2009) were assessed for the Huangpu
River floodplain where the city of Shanghai is located. A 2D hydrodynamic model (FloodMap-Inertial)
was used to estimate the flood risks associated with each scenario. Flood events with various return
periods (10-, 100- and 1000-year) were designed based on a one in 50 year flood event that occurred in
Shanghai on August 1997.
Results demonstrate the individual as well as the combined impacts of the three anthropogenic factors
on the changing fluvial flood risks in the Huangpu River basin over the last three decades during the
city’s transitional economy (1979–2009). Land subsidence and urbanization were found to lead to proportionate
but non-linear impact on flood risks due to their complex spatial and temporal interaction. The
impacts and their sensitivity are the function of the rate and spatial distribution of each evolving factor.
While the pattern of response to individual anthropogenic variables is largely expected, the combined
impacts demonstrate greater spatial and temporal variation. Flood defences offer considerable benefits
in reducing the total inundated areas in the Huangpu River basin over the periods considered, for all
magnitude floods. This, to a large extent, alleviates the adverse impacts arising from land subsidence and
urbanization.

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This paper was supported by the National Natural Science Foundation
of China (Grant nos: 41201550, 41371493, 71373084), the
Humanities and Social Science Project of Education Ministry (Grant
no: 12YJCZH257), Innovation Program of Shanghai Municipal Education
Commission (Grant nos: 13YZ061, 13ZZ035), the Open
Research Fund of State Key Laboratory of Estuarine and Coastal
Research (Grant no: SKLEC-KF201407), Key Project of Young Talent
Foundation from Zhejiang Gongshang University (Grant no:
QZ13-2).